MRI, because of its high tissue contrast and spatial resolution as well as multiplanar and functional imaging capabilities, has the most appeal for monitoring and controlling therapy. Open magnets, which allow some sort of access to the patient and are equipped with a navigation system, can provide an interactive environment in which biopsies, percutaneous or endoscopic procedures, and minimally invasive interventions or open surgeries can be performed. In addition, various thermal ablations with image-based control of energy deposition can be performed to exploit the intrinsic sensitivity of MRI to both temperature and tissue integrity. The drawback of using interventional open MR is that, almost all of the introduced open magnets are low field and in turn the quality of the images are considerably lower comparing to high field closed magnet counterparts. Therefore, for a number of procedures, where the tissue contrast and quality of the image is vital, the low field MR, although greatly facilitates the tissue/lesion localization, cannot be effectively utilized.
Indeed, in breast cancer, prostrate cancer and brain tumor procedures, preoperative imaging depicts tumor extent better because of the ability to perform dynamic imaging, parametric modeling, and diffusion or other functional MR imaging methods with acquisition times that would be impractical for interactive intra-procedural imaging. The ultimate goal in these procedures would be to have both the fast acquisition and patient accessibility of the open magnet interventional MR and the image quality and tissue contrast of the closed magnet MR.
Interventional and surgical procedures require the physician to have access to updates about the patient anatomy or changing position of movable organs. Near real-time imaging during intervention (without registration) establish the necessary relationship between the patient and the images. The lower image quality of the open magnets prohibits their usage for a variety of the procedures. There is a need for a registration procedure, which augments open magnet intra-operative image (volume is considered to be three-dimensional image and is referred to as image hereafter) with high quality pre-operative images from conventional high field magnet MRI system.